Add documentation for vertex time reconstruction

Follow up to !69290 (merged) and !69404 (merged) to document information regarding vertex time.

/cc @aleopold @dshope

assigned to @jedebevc

build area is cleaned as the previous build was for the MR labeled as full-build

This merge request affects 1 package:

• HighGranularityTimingDetector/HGTD_Reconstruction/HGTD_RecAlgs

This merge request affects 1 file:

• HighGranularityTimingDetector/HGTD_Reconstruction/HGTD_RecAlgs/README.md

Adding @cohm ,@lshan ,@goetz ,@dshope as watchers

added HGTD main review-pending-level-1 labels

The system determined that the changset affects text files and cancelled CI integration tests

CI Result SUCCESS (hash fb723242)

	Athena
externals
cmake
make
tests

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Athena: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-EL9 7877] (remote access info)

The changes are straightforward and there are no issues with the CI. Approving from L1.

added review-approved label and removed review-pending-level-1 label

merged

mentioned in commit 3fb05c88